One of the most important steps in optimizing and tuning mysql is to identify the queries that are causing problems. How can we find out what queries are taking a long time to complete? How can we see what queries are slowing down the mysql server? Mysql has the answer for us and we only need to know where to look for it ...
Normally from my experience if we take the most 'expensive' 10 queries and we optimize them properly (maybe running them more efficiently, or maybe they are just missing a simple index to perform properly), then we will immediately see the result on the overall mysql performance. Then we can iterate this process and optimize the new top 10 queries. This article shows how to identify those 'slow' queries that need special attention and proper optimization.